Compounds such as 1,1,1,3,3,3-hexafluoropropane (i.e., HFC-236fa) have found uses as refrigerants, fire extinguishants, heat transfer media, gaseous dielectrics, sterilant carries, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. More particularly, HFC-236fa itself is a highly effective and environmentally acceptable fire extinguishant and refrigerant.
Canadian Patent No. 2,073,533 discloses a liquid phase process for the manufacture of HFC-236fa by contacting HCC-230fa with HF in the presence of a liquid phase catalyst (e.g., tin and antimony compounds). All of the 1,1,1,3,3,3-hexachloropropane is converted to 1-chloro-1,1,3,3,3-pentafluoropropane (i.e., HCFC-235fa) and HFC-236fa with a selectivity of greater than 45 mole % with respect to HFC-236fa. The separation of pure HFC-236fa is complicated by the presence of HCFC-235fa. Moreover, vapor processes are often preferred because operational advantages (e.g., HF corrosivity problems ware typically exacerbated in the liquid phase).
U.S. Pat. No. 5,414,165 discloses a vapor phase process for the manufacture of HFC-236fa by contacting HCC-230fa (and sufficient haloprecursors of HFC-236fa) with HF in the presence of a trivalent chromium catalyst.
CCl.sub.3 CH.sub.2 CCl.sub.3 (HCC-230fa) is a high boiling liquid (b.p. 206.degree. C. at 101.3 kPa). Efficient use of a catalytic vapor phase reactor requires that HCC-230fa be fed to the reactor as a vapor. Feeding liquid directly to a catalyst bed is well known in the art to cause deactivation of the catalyst. Evaporation of HCC-230fa in a vaporizer of standard design can cause substantial degradation to HCl, CCl.sub.3 CH.dbd.CCl.sub.2, and in particular, undesirable higher boiling materials such as chlorinated six-carbon compounds and tars. Furthermore, the fluorine-chlorine exchange reaction is typically highly exothermic. Replacing all six chlorines of HCC-230fa with fluorine to produce HFC-236fa in the catalytic reactor can cause heat management problems.